Boston (AP) — A group of Massachusetts residents opposed to casinos are challenging the sale of state property to Wynn Resorts.

A lawsuit filed in state Superior Court on Monday asserts that the Massachusetts Bay Transportation Authority failed to comply with the state's public bidding law when it proposed selling some $6 million worth of land to Wynn for its $1.7 billion casino project on the Everett waterfront.

The suit, which asks a judge to void the sale, was filed by 30 state taxpayers including leaders of last year's failed effort to repeal the state's casino law.

Wynn spokesman Michael Weaver maintains the land deal followed a "clear and open" public bid process, pointing to advertisements placed in local newspapers and the Secretary of the Commonwealth's registry in September 2014.

But the lawsuit suggests officials representing the MBTA, Wynn and the city of Everett were in discussions to convey the property without a public bid as early as 2013.

The casino opponents also dismiss the state's bidding process as "truncated," noting that the MBTA gave just a month for responses as it sought bids to best Wynn's $6 million offer.

They also state that the MBTA had already executed a purchase offer with Wynn and accepted a $1.5 million deposit by then. The casino company needs the roughly 1.8 acres of land, which houses MBTA storage and repair facilities, for an entry to its roughly 30-acre development site.

The lawsuit also suggests the MBTA land was worth as much as $30 million and had been sold to Wynn at far less than fair market value. Wynn maintains it paid a "premium price" for the land, buying it for $78.35 per square foot when it was appraised at $50 per square foot.

"It has been misrepresented that the land was worth $30 million, however that was for a significantly larger parcel and project than the 76,578 square feet that Wynn eventually purchased for $6 million," said Weaver, the company spokesman.

The MBTA declined to comment on the lawsuit, which comes as the cities of Boston, Revere and Somerville have each independently filed lawsuits against the state Gaming Commission seeking to overturn its decision to grant Wynn the lucrative Boston-area gambling license.

Mohegan Sun, which vied for the license with a project it proposed in Revere, is a party to Revere’s suit.